ISSN(Print) 1975-0102
ISSN(Online) 2093-7423
J Electr Eng Technol Vol. 8, No. ?: 742-?, 2013
http://dx.doi.org/10.5370/JEET.2013.8.?.742
The Study of the Stray Load Loss and Mechanical Loss of Three Phase
Induction Motor considering Experimental Results
Dong-JunKim*, Jae-Hak Choi*, Yon-Do Chun*, Dae-Hyun Koo*
and Pil-Wan Han†
Abstract – The accurate determination of induction motor efficiency depends on the estimation of the
five losses of stator and rotor copper loss, iron loss, mechanical loss and stray load loss. As the
mechanical and stray load losses are not calculated by electro-magnetic analysis, the values of these
two losses are very important in induction motor design. In this paper, the values of mechanical loss
and stray load loss are proposed through investigating testing data from commercial products of three
phase induction motors under 37kW. If the values of this paper are applied to motor design, the
accuracy of design and analysis can be improved. The losses of motors are obtained by using load and
no-load test results following IEC 60034-2-1 standard.
Keywords : Stray load loss, Mechanical loss, Efficiency, Induction motor
1. Introduction
2007. One method of this standard followed the IEEE
112B procedure of determining the SLL through test
measurements. This standard also provided for assigning
the value of stray loss as a percentage of input power
which is dependent on motor output power [2].
The representative standards for efficiency test of three
phase induction motor are IEEE std. 112, IEC 60034-2-1
and CSA C 390, where the stray load loss (PS) is
determined by the means of output power. These standards
also determine the PS from assigned values in pre-defined
curve, which depend on motor rated output power [1]. The
PS is determined by subtracting the conventional losses
from the apparent total loss. The dependence of the PS on
motor rating is often stated in literature but the analytical
calculation of PS is difficult and historical test data have
often been relied upon [2].
In squirrel-cage induction motors, the mechanical losses
are produced by friction losses in bearings, windage losses
of outside cooling fan, friction air losses of rotor and
windage losses of internal fans of rotor rings [3]. In IEC
60034-2-1 and IEEE 112B standard, the mechanical loss is
determined from no-load operation of the motor at variable
voltage [4].
In this paper, the values of mechanical loss and stray
load loss are investigated through testing data from 196
commercial products of three phase induction motors under
37kW
2.1 Procedure of efficiency test
The test procedure for efficiency and losses is listed in
Table 1.
The load test is applied at six different load points. The
first four load points should be chosen to be approximately
equally spaced between not less than 25% and up to and
including the 100% load. The remaining two load points
should be suitably approximately equally spaced above
100%. In no-load test, test motor is uncoupled from the
loading device and operated at a minimum number of 7
values of voltage ranging from 125% of the rated voltage
to 20% [4].
2.2 Efficiency and mechanical loss calculation
Motor efficiency, η is defined as a ratio of output
mechanical power to the input electrical power
(1)
2. Efficiency Test by IEC 60034-2-1
Table 1. Efficiency test procedure
2.1 D2L sizing equation
Order
1
2
3
4
5
6
IEC 60034-2-1 was approved to replace IEC 60034-2 in
†
Corresponding Author: Electric Motor Research Center, Korea
Electrotechnology Institute (pwhan@keri.re.kr)
*
Electric Motor Research Center, Korea Electrotechnology Institute
(pwhan@keri.re.kr)
Received: February 25, 2013; Accepted: July 19, 2013
742
Procedure
Check of motor specification
Measurement of motor resistance
Rated load thermal test
Load test
No load test at variable voltage
Calculation of losses and efficiency
D
Dong-JunKim,
J
Jae-Hak
Choi, Yon-Do
Y
Chun, Dae-Hyun
D
Koo and Pil-Wan H
Han
Fig. 1.
1 Plot to deterrmine mechannical loss
Fig
g. 2. Plot to determine strayy load loss (op
ptimum model)
where Ploss is the
w
t total lossees in the motoor including stator
(P
Pc1) and rotorr copper loss (Pc2), iron losss(Pi), mechannical
looss (Pm) and stray load loss (Ps). Thhe core loss and
m
mechanical
looss are dettermined undder the no--load
opperation. The stator, rotor and
a stray lossses are determ
mined
unnder load teests, wherebyy the motor is coupled to
t a
dyynamometer.
The stator loss is meassured as I2R loss in the stator
w
winding.
The rotor
r
copper loss
l
is determ
mined as a prooduct
off the slip (s) and
a the airgap power in Eq. (5).
×
×s
Tab
ble 2. Load tesst results of 377kW 4polemo
otor
Ou
utput power/
rated
r
[%]
To
orque[Nm]
Input[kW]
Current[A]
C
Sp
peed[rpm]
Tem
mperature of
winding[°C]
Voltage[V]
V
(2)
_
110
100
75
50
25
2449.9
4
49.9
8
85.6
1767
219.4
43.7
75.9
1772
199.1
39.6
69.3
1775
148.8
29.6
54.2
1780
98.8
19.9
40.4
1788
49.22
10.33
29.33
17933
1001.6
101.8
101.6
99.6
98.3
96.77
3880.9
379.8
380.4
379.6
380.5
380.33
Tab
ble 3. No-loadd test results of 37kW 4poleemotor
In
nput voltage/
rated [%]
Voltage[V]
current[A]
Input[kW]
In Eq. (3), subtracting the
t no-load stator
s
copper loss
(P
Pc1_0) from noo-load input power (Pin_0) gives a consstant
looss (Pk) whichh is the sum off mechanical and
a core loss. Fig.
1 shows the pllot between Pk and the volltage squared (V2)
t results off 37kW inducttion motor (T
Table
frrom no-load test
3)). Extrapolating a straight line to zero voltage, the zero
vooltage axis inttercept is the mechanical
m
looss (Pm) [4].
_
1
125
125
100
80
60
50
5
35
200
475
45.0
2.21
380
24.8
0.88
3304
118.0
00.64
228
12.8
0.49
19
90
10
0.5
0.45
133
7.4
0.38
766
5.00
0.31
Y
(3)
((5)
(
(6)
Fig.
F 4 shows the
t residual loosses at six lo
oad points (PL),
regrression line (Y
Y) and PS of opptimum modeel.
Tables
T
1 and 3 show the loaad test and no--load test resuults
of 37kW
3
4-pole induction motor respectiveely to determine
the losses.
2.3 Stray load
d loss calculaation
In the IEEE standard 1122B and the IE
EC 60034-2-1, the
sttray load losss (Ps) is deetermined byy subtracting the
coonventional loosses from thee apparent tottal loss (Papp). The
appparent total loss is the difference beetween the input
i
poower and outpput power at thhe load point of interest
2.4 Assigning vaalues of strayy load loss
The
T IEC 60034-2-1 standarrd also allows for assigningg a
valu
ue for the strayy load loss. T
This value is dependent on the
t
mottor rating and is between 0..5% and 2.5%
% of input pow
wer
in Eq.
E (7) [2, 4]. Table
T
4 showss the assigned
d values of IEE
EE
std. 112 [5], whicch are the perrcentage of ou
utput power annd
cann
not be comppared with IIEC 60034-2-1 exactly but
b
sim
milar to assigned values of IEC 60034-2--1 of Eq. (7) in
outlline.
(4)
where PL is thee residual losss. The residual loss data at
w
a six
looad points shall
s
be sm
moothed by using
u
the liinear
reegression metthod based on
o expressingg the losses as a
fuunction of the square of thee load torque in
i Eq. (5) wheere A
(sslop) and B (ooffset) are connstant coefficients. The offsset B
iss removed to obtain
o
the corrrect stray loadd loss. The loppe is
used to calculaate the stray looad loss using Eq. (6) [4, 5]..
Ps = 0.025P1 for Pn ≤ 1kW
743
The Studdy of the Stray Load
L
Loss and Mechanical
M
Loss of Three Pha
ase Induction Motor
M
considerinng Experimenta
al Results
T
Table
4. Assignned value for stray load loss (IEEE std. 112)
1
Rated outpput power (Pn) [kkW]
1 ~ 90
91 ~ 375
3 ~ 1850
376
1851 and
a greater than
Ps/Pn [%]
1.8
1.5
1.2
0.9
⎡
⎛ P ⎞⎤
Ps = ⎢ 0.025 − 0.005 log10 ⎜ 2 ⎟ ⎥ P1
⎝ 1kW ⎠ ⎦
⎣
for 1kW < Pn < 10000kW
Ps = 0.005P1
(7)
for Pn ≥10000kW
W
Fig. 5. Stray
S
load losss distribution (6Pole)
(
3. New Assiigned Valuees of Stray Load
L
Loss an
nd
Mechan
nical Loss
mottors, 85 4-polee motors and 559 6-pole mottors.
In
n these grapphs, red linee (Average) represents the
t
averrage value off stray load looss (PS) acco
ording to outpput
pow
wer and trianggle-green line is the assigneed value of IE
EC
600
034-2-1 calculated by Eq. (77). Most of thee test values are
a
low
wer than assiggned value off IEC 60034-2
2-1. The circlleblacck line is thee value propoosed by consiidering test annd
averrage value in this paper whhich is moved
d by 1.0% froom
the assigned valuue of IEC 600034-2-1. As shown in theese
grap
phs, it is know
wn that the sttray load losss is not affectted
by the
t number off poles.
3.1. Stray load loss
Figs. 3, 4, annd 5 show thee distribution of stray load loss
off induction motors
m
under 37kW tested by
b IEC 60034--2-1.
A test motorss have 380V or
All
o 460V/60Hzz rating whichh are
m
made
by motoor manufactuurers and tested for veriffying
effficiency in teesting laborato
ory of Korea Electrotechno
E
ology
R
Research
Instittute. The dataa set is comprrised of 52 2--pole
3.2.. Mechanicall loss
Figs.
F
7, 8, and 9 are the distrribution of meechanical lossses
of in
nduction motoors under 37kW
W of section 3.1.
3
In
n Fig. 7, the mechanical losses of 2 pole
p
motors are
a
high
her than those of 4 and 6 pole motors because of the
t
high
hest speed in the
t line start innduction. Thee average valuues
are about 3% of output powerr under 5.5kW
W rating and 1.5
1
% above
a
10KW rating.
r
In this paper, the meechanical lossses
are proposed as Eq.
E (8) using ttest and averag
ge values.
Fig.
F 8 shows thhe mechanicall losses of 4 pole motors. The
averrage values are about 1.55% of outpu
ut power undder
2.2k
kW rating andd 1.0% above 3.7kW rating
g. The proposed
valu
ue is expressed by Eq. (9)
Fig. 3. Stray load looss distribution (2Pole)
Fig. 6. Mechanical
M
loss distribution (2Pole)
Fig. 4. Stray load looss distribution (4Pole)
744
D
Dong-JunKim,
J
Jae-Hak
Choi, Yon-Do
Y
Chun, Dae-Hyun
D
Koo and Pil-Wan H
Han
Tab
ble 5. Relationn between straay load loss an
nd material coost
(15kW 4pole
4
motor)
2.2
3.7
0.01 ,
0.005
0.005 ,
5
5.5
0.000909
, 5.5
11
,
(8)
,
(9)
5.5
244
210
60%↓
18%↓
13.9%
%
↓
91% (IEC 600
034-2-1)
0.91% (Propossed value)
The
T mechaniccal loss of liine start indu
uction motor is
affeected mostly by
b cooling fann. The cooling
g fan size has to
decrrease to reduuce mechaniccal loss, whille the arbitraary
redu
uction of coolling fan size results in moto
or performancces
mallfunction due to the rise in the operating temperature. In
this reason, it is important to design or sellect the coolinng
fan by consideriing the mechhanical loss and cooling in
mottor design.
The
T two cooliing fans of Fig. 9 have th
he different siize
and
d these are forr 3.7kW 2-pole motor. Thee efficiency teest
resu
ults are shownn in Table 6 w
whose cooling fans are applied
to the
t same mootor. In this rresults, we can
c see that an
appropriate selecction of coolinng fan make a contribution to
imp
prove a motoor efficiency. The temperrature rising of
mottor using fan II is increasedd by 5 degreee, which can be
b
Fig. 9 showss the mechaniccal losses of 6 pole motors. The
avverage valuess are about 1.0% of outtput power under
u
5.5kW rating and
a 0.5% aboove 11kW ratiing. The proposed
vaalue is expressed by Eq. (100)
0.015 ,
2.2
0.015 0.0033
2.2
0.01 ,
3
3.7
[k￦]]
Stray load loss(PS)
PS/Input poweer
Test efficiencyy
Volume
Activematerial cost
c
(stteel+copper+alum
minum)
Assigned
A
value off stray
load loss
Remarkk
4.2.. Mechanicall loss
Fig. 8.Mechanical
.
looss distributioon (6Pole)
5.5
11
Motor
M
(B)
100
0.61
90.8
82
Unit
efficciency, volum
me and active material cost between 15kkW
com
mmercial motoors of manufaacturer A and B. Motor B has
h
low
wer stray load loss by 660% than motor
m
B and it
con
ntributes to low
wer volume aand active maaterial cost. The
straay load loss off motor A is 1..48% of input power whichh is
closse to the assigned value (1.91%) of IEC
I
60034-2--1,
whiile those of motor
m
B is 0.61% close to
t the proposed
valu
ue (0.91%) off this paper. A
As the materiaal cost of mottor
incrreases for highher efficiencyy, it becomes more
m
significaant
to reduce the cosst in design annd manufacturring process. As
A
show
wn in Table 5,
5 the assigneed value of IE
EC 60034-2-1 is
slightly higher thhan test resultts of commerccial motor thuus,
the new assignedd value is exxpected to be more useful in
mottor developmeent.
Fig. 7. Mechanical loss
l
distributioon (4Pole)
0.03 ,
5
5.5
0.03 0.00273
5.5
0.015 ,
7.5
[W]
[%]
[%]
[%]
Motor
(A)
250
1.48
91.1
100
Items
11
(10)
4 Effects of Stray Load Loss and Mechanical
4.
M
L
Loss
M
Design
n and Perforrmance
to Motor
4.1. Stray load loss
Table 5 shoows the compparison of thee stray load loss,
Fig. 9. Cooling faan (3.7kW 2po
ole)
745
The Studdy of the Stray Load
L
Loss and Mechanical
M
Loss of Three Pha
ase Induction Motor
M
considerinng Experimenta
al Results
T
Table
6. Motor efficiency teest results acccording to coooling
m
fan (3.7kW 2pole motor)
Losss[W]
Temp.
rising
Stator Rootor Mech.
ΔT Irron copper coppper (Pm/Pn)
F
Fan
Eff.
[%]
Currrent
[A
A]
I
85.2
8..04
30
173
137
9
98
204
(5.5%)
29
II
87.8
7..87
35
169
133
7
74
98
(2.6%)
41
[6]
Stray
S
l
load
[7]
[8]
im
mproved by making
m
fan larger
l
considdering approppriate
m
mechanical
losss or reducing copper loss annd iron loss.
5. Con
nclusion
B
Dong-Jun
n Kim He received B.S
degree inn electrical engineering in
2004 from
m Kyungnam University. He
H
received M.S degreee in electriccal
engineerinng in 2013 frrom Changwoon
National U
University. Hee has worked at
Korea E
Electrotechnology Researrch
Institute ((KERI). He is currently a
seniior Engineer of
o Electric Mootor Research Center, KERII.
As the mecchanical loss and stray looad loss are not
caalculated by electro-magnnetic analysis and affectedd by
m
manufacturing
process or mechanical
m
strructure, it is very
diifficult to exppect these lossses in designn process. In this
paaper, assignedd values of mechanical
m
looss and stray load
looss are propossed under 37kW
W by using teest results.
As shown inn test results of
o commerciall motors, the stray
s
looad losses disttribute variously but these are
a lower thann the
asssigned valuees of IEC 600034-2-1. If asssigned valuees of
IE
EC 60034-2-11 are used in motor designn, motor could be
ovver-sized due to stray load loss bigger thhan in practice. In
thhis reason, thhe new assignned values of
o stray load loss
coould be a guiideline for motor
m
manufaccturers who trry to
reeduce the mateerial costs.
In case of thhe mechanicall losses, if thee proposed vaalues
arre used in mootor design, it is expected to be helpful for
deeveloping hiigh efficienccy motor annd selecting fan
sppecification.
S.,
Jae-Hak Choi He recceived the B.S
M.S., andd Ph.D. degrees in Electriccal
Engineerinng from Hany
yang Universiity
in 1999, 22001 and 200
05 respectively.
From 2005 to 2007, hee worked at LG
L
electronicss. Since 2008, he has workked
at Korea Electrotechno
ology Researrch
Institute ((KERI). He is currently a
seniior researcherr of Electric M
Motor Research
h Center, KER
RI.
Refeerences
[11]
[22]
[33]
[44]
[55]
Polyphase Induction
I
Mottors and Geneerators,” 2004.
A. Bogliettti, “Impact off the Supply Voltage on the
t
Stray-Load Losses in Indduction Motorrs”, IEEE Tranns.
on Ind. Apppl., vol. 46, noo. 4, pp. 1374--1380, 2010.
K. Bradleyy, “Evaluatioon of Stray Load Loss in
Induction Motors
M
with a Comparison of Input-Outpput
and Caloriimetric Methoods”, IEEE Trans. on Innd.
Appl., vol. 21, no. 3, pp. 682-689, 200
06.
A. Boglieetti, “Internaational Stand
dards for the
t
Induction Motor
M
Efficieency Evaluatiion: A Criticcal
Analysis of
o the Stray-Load Loss Determination
D
n”,
IEEE Transs. on Ind. Apppl., vol. 40, no.
n 5, pp. 129941301, 2004.
S.,
Yon-Do C
Chun He received the B.S
M.S. and Ph.D. degrees in electriccal
Engineerinng from Hany
yang Universiity
in 1996, 11998 and 200
01, respectively.
From 20001 to 2003, he received a
Japan Socciety for the Promotion of
Science (JJSPS) fellowship and he was
w
with the Department of Electriccal
Eng
gineering at Waseda
W
Univversity as a visiting
v
scholar.
From
m 2004 to 2012,
2
he hass worked at Korea Electrrotech
hnology Reseearch Institutee (KERI). Hee is currentlyy a
chieef researcher, Principal Ressearcher and technical
t
leadder
of Electric
E
Motorr Research Ceenter, KERI.
A. T. de Almeida,
A
F. T. E. Ferreira, J.
J F. Busch, annd P.
Angers, “Comparative
“
e analysis of IEEE 112-B and
IEC 34-22 efficiency tessting standardds using stray load
losses inn low voltagge three-phasee cage inducction
motors”, IEEE Trans. Ind. Appl., vol.
v 38, no. 2, pp.
608-614, Mar./Apr. 20002.
E.B. Agaamloh, “An Evvaluation of induction macchine
stray loadd loss from coollated test ressults”, IEEE Trans.
T
Ind. Appll., vol. 46, no. 6, pp. 2311-22318, Nov. 2010.
T.A. Lipo, “Introducttion to AC Machine
M
Desiign”,
Wisconsiin Power Electronics
E
R
Research
Ceenter,
Universitty of Wisconsiin, 2004, pp 302-304.
IEC 600334-2-1, “Stanndard methodss for determiining
losses annd efficiency from
f
tests (exxcluding machhines
for tractioon
IEEE Stdd. 112, “IEEE
E Standard Test
T Proceduree for
746
Dong-JunKim, Jae-Hak Choi, Yon-Do Chun, Dae-Hyun Koo and Pil-Wan Han
Dae-Hyun Koo He received the B.S.
and M.S. degrees in Electrical Engineering from Hanyang University in
1989 and 1991, respectively. From
1991, he has worked at Korea Electrotechnology Research Institute (KERI).
In 2002, he received Ph. D. degree
from Dong-A University. He is
currently a director of Electric Motors Research Center,
KERI.
Pil-Wan Han He received the B.S.,
M.S. and Ph.D. degrees in Electrical
Engineering from Hanyang University
in 1998, 2000 and 2013 respectively.
From 2000 to 2005, he worked at LG
electronics. Since 2005, he has worked
at Korea Electrotechnology Research
Institute (KERI). He is currently a
senior researcher of Electric Motor Research Center, KERI.
747